Expose new T5Manager signal enabling glasses events to be cancelled

[Jonathan-Stevens]

This change adds a signal to T5Manager that fires when evaluating new glasses in ShouldUseGlasses().
Scripts that subscribe to this event can observe the glasses ID of an incoming pair of glasses and opt to cancel the connection attempt. This is useful for applications that might want to restrict/vary the number of glasses they support or otherwise ignore a specific glasses ID.

[patrickdown]

Would you mind rebasing these changes onto the current main so that the github CI can run?

[patrickdown]

This should probably extend RefCounted instead of Object

[patrickdown]

So, this is my fault for not making good documentation for this but the way I originally intended for this to be handled was for the user to derive their own T5Manager subclass. So the user would just create there own subclass and override ShouldUseGlasses.

This use of Signal in this case is a little odd since they are multi cast. They are generally used to tell other parts of the system about an event but not generally to pass back information.

I think there are good things which could be added to the default T5Manger. For example an numeric field that allows the user to select the maximum number of glasses that are allowed to connect. A string array could also be added to hold the glasses IDs that could be allowed to connect or the preferred order.